There is substantial interest in reducing the weight of parts used to manufacture vehicles such as automobiles, trucks, airplanes and boats for the purpose of improving fuel economy. One approach to reducing the weight of parts is to use light weight/high strength aluminum alloys to manufacture parts. The yield strength of parts made of some aluminum alloys may be increased by aging the parts over a substantial period of time. Waiting for natural aging to occur is generally not economical feasible in manufacturing processes due to the long period of time required to strengthen the parts.
Aging may be accelerated by heating the parts in a process referred to as “artificial aging.” For example, parts made of AA6xxx series aluminum may be artificially aged by heating the parts, for example to 225° C. for a period of 30 minutes to double the yield strength of the parts. After heating, the parts are cooled and may be chemically treated by applying a conversion coating and/or removal of oxidation from the surface of the parts in preparation for painting.
Parts made of aluminum alloys may be pre-formed in bending operations and hydro-forming operations. After forming, the parts may be trimmed, punched and de-burred before artificial aging to increase the yield strength. The parts are more malleable before artificial aging and easier to bend, hydro-form, cut and trim.
One problem with artificial aging is that it is impossible to determine by visual inspection whether the parts were subjected to the artificial aging process. A second problem is that raw material may have an age limit after which it cannot be reliably processed into a quality part. A tensile test may be used to verify the yield stress of a part but a tensile test is destructive to the part. While a hardness test could be used to test for artificial aging, hardness test results may not be an accurate predictor of yield stress, is time consuming, and adds expense to the manufacturing process.
Structural beams, such as pillars, roof rails, frame parts, and the like once assembled to a vehicle may be located in inaccessible areas that cannot be readily checked for yield strength. These types of structural parts may be in areas of the vehicle that are tested for crashworthiness such as bumper structures, passenger compartment beams and pillars, roof supports and the like. The yield strength of such parts may be critical to vehicle durability and/or vehicle quality. If it is determined that such structural parts lack the specified strength characteristics after the fact, replacing the parts is not easily accomplished and may result in scrapping the entire vehicle.
This disclosure is directed to solving the above problems and other problems as summarized below.